M. Baranov - Academia.edu (original) (raw)

Papers by M. Baranov

Research paper thumbnail of Observability of Quantum Criticality and a Continuous Supersolid in Atomic Gases

Physical Review Letters, 2010

We analyze the Bose-Hubbard model with a three-body hard-core constraint by mapping the system to... more We analyze the Bose-Hubbard model with a three-body hard-core constraint by mapping the system to a theory of two coupled bosonic degrees of freedom. We find striking features that could be observable in experiments, including a quantum Ising critical point on the transition from atomic to dimer superfluidity at unit filling, and a continuous supersolid phase for strongly bound dimers.

Research paper thumbnail of Quantum gases in trimerized kagomé lattices

Physical Review A, 2005

We study low temperature properties of atomic gases in trimerized optical kagomé lattices. The la... more We study low temperature properties of atomic gases in trimerized optical kagomé lattices. The laser arrangements that can be used to create these lattices are briefly described. We also present explicit results for the coupling constants of the generalized Hubbard models that can be realized in such lattices. In the case of a single component Bose gas the existence of a Mott insulator phase with fractional numbers of particles per trimer is verified in a mean field approach. The main emphasis of the paper is on an atomic spinless interacting Fermi gas in the trimerized kagomé lattice with two fermions per site. This system is shown to be described by a quantum spin 1/2 model on the triangular lattice with couplings that depend on the bond directions. We investigate this model by means of exact diagonalization. Our key finding is that the system exhibits non-standard properties of a quantum spin-liquid crystal: it combines planar antiferromagnetic order in the ground state with an exceptionally large number of low energy excitations. The possibilities of experimental verification of our theoretical results are critically discussed.

Research paper thumbnail of Ultracold Dipolar Gases ? a Challenge for Experiments and Theory

Physica Scripta, 1999

We present a review of recent results concerning the physics of ultracold trapped dipolar gases. ... more We present a review of recent results concerning the physics of ultracold trapped dipolar gases. In particular, we discuss the Bose-Einstein condensation for dipolar Bose gases and the BCS transition for dipolar Fermi gases. In both cases we stress the dominant role of the trap geometry in determining the properties of the system. We present also results concerning bosonic dipolar gases in optical lattices and the possibility of obtaining variety of different quantum phases in such case. Finally, we analyze various possible routes towards achieving ultracold dipolar gases. * This paper is based on the lecture given by M. Lewenstein at the Nobel Symposium "Coherence and Condensation in Quantum Systems", Gothesburg, 4-7.12.2001.

Research paper thumbnail of Quantum phases of Bose-Fermi mixtures in optical lattices

Research paper thumbnail of Phase transitions driven by competing interactions in low-dimensional systems

EPL (Europhysics Letters), 2010

Variable-temperature scanning tunnelling microscopy is used to study an orderorder phase transiti... more Variable-temperature scanning tunnelling microscopy is used to study an orderorder phase transition in a virtually defect-free quasi-one-dimensional surface system. The phase transition is driven by competing electronic interactions. The phase diagram is captured by a modified Landau formalism containing a coupling term between two different subsystems. The extra term has the effect of a spontaneously generated field which drives the phase transition. The proposed formalism applies to a variety of problems, where competing interactions produce sometimes counter-intuitive ordering phenomena.

Research paper thumbnail of Electronically driven phase transitions in a quasi-one-dimensional adsorbate system

The European Physical Journal B, 2010

A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface res... more A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface resonance structure is studied by angle-resolved photoemission spectroscopy for the clean surface as well as for different Bromine coverages. A Fermi surface mapping reveals saddle points at the Fermi level in the interior of the surface Brillouin zone. Correspondingly, a maximum in the static response function χ(q, 0) at the connecting vector q is expected. With 1/2Gx < q < 2/3Gx one observes indeed a 3-fold periodicity around defects and a 2-fold periodicity at low temperature for ΘBr = 0.5 ML. Cooling of a defect-free c(2 × 2)−Br/Pt(110) preparation counter-intuitively results in a loss of long-range order. Motivated by DFT calculations this is attributed to an anomalous order-order phase transition into the (2 × 1) phase accompanied by intense, strongly anisotropic fluctuations within a temperature range of ∼200 K. The peculiar behaviour is rationalised in terms of a competition between inter-adsorbate repulsion and an adsorbate triggered 2kF interaction in the substrate.

Research paper thumbnail of Magnetism and domain formation in SU(3)-symmetric multi-species Fermi mixtures

New Journal of Physics, 2011

We study the phase diagram of an SU(3)-symmetric mixture of threecomponent ultracold fermions wit... more We study the phase diagram of an SU(3)-symmetric mixture of threecomponent ultracold fermions with attractive interactions in an optical lattice, including the additional effect on the mixture of an effective three-body constraint induced by three-body losses. We address the properties of the system in D ≥ 2 by using dynamical mean-field theory and variational Monte Carlo techniques. The phase diagram of the model shows a strong interplay between magnetism and superfluidity. In the absence of the three-body constraint (no losses), the system undergoes a phase transition from a color superfluid phase to a trionic phase, which shows additional particle density modulations at half-filling. Away from the particle-hole symmetric point the color superfluid phase is always spontaneously magnetized, leading to the formation of different color superfluid domains in systems where the total number of particles of each species is conserved. This can be seen as the SU(3) symmetric realization of a more general tendency to phase-separation in three-component Fermi mixtures. The three-body constraint strongly disfavors the trionic phase, stabilizing a (fully magnetized) color superfluid also at strong coupling. With increasing temperature we observe a transition to a non-magnetized SU (3) Fermi liquid phase. arXiv:1012.4499v2 [cond-mat.quant-gas]

Research paper thumbnail of Observability of Quantum Criticality and a Continuous Supersolid in Atomic Gases

Physical Review Letters, 2010

We analyze the Bose-Hubbard model with a three-body hard-core constraint by mapping the system to... more We analyze the Bose-Hubbard model with a three-body hard-core constraint by mapping the system to a theory of two coupled bosonic degrees of freedom. We find striking features that could be observable in experiments, including a quantum Ising critical point on the transition from atomic to dimer superfluidity at unit filling, and a continuous supersolid phase for strongly bound dimers.

Research paper thumbnail of Quantum gases in trimerized kagomé lattices

Physical Review A, 2005

We study low temperature properties of atomic gases in trimerized optical kagomé lattices. The la... more We study low temperature properties of atomic gases in trimerized optical kagomé lattices. The laser arrangements that can be used to create these lattices are briefly described. We also present explicit results for the coupling constants of the generalized Hubbard models that can be realized in such lattices. In the case of a single component Bose gas the existence of a Mott insulator phase with fractional numbers of particles per trimer is verified in a mean field approach. The main emphasis of the paper is on an atomic spinless interacting Fermi gas in the trimerized kagomé lattice with two fermions per site. This system is shown to be described by a quantum spin 1/2 model on the triangular lattice with couplings that depend on the bond directions. We investigate this model by means of exact diagonalization. Our key finding is that the system exhibits non-standard properties of a quantum spin-liquid crystal: it combines planar antiferromagnetic order in the ground state with an exceptionally large number of low energy excitations. The possibilities of experimental verification of our theoretical results are critically discussed.

Research paper thumbnail of Ultracold Dipolar Gases ? a Challenge for Experiments and Theory

Physica Scripta, 1999

We present a review of recent results concerning the physics of ultracold trapped dipolar gases. ... more We present a review of recent results concerning the physics of ultracold trapped dipolar gases. In particular, we discuss the Bose-Einstein condensation for dipolar Bose gases and the BCS transition for dipolar Fermi gases. In both cases we stress the dominant role of the trap geometry in determining the properties of the system. We present also results concerning bosonic dipolar gases in optical lattices and the possibility of obtaining variety of different quantum phases in such case. Finally, we analyze various possible routes towards achieving ultracold dipolar gases. * This paper is based on the lecture given by M. Lewenstein at the Nobel Symposium "Coherence and Condensation in Quantum Systems", Gothesburg, 4-7.12.2001.

Research paper thumbnail of Quantum phases of Bose-Fermi mixtures in optical lattices

Research paper thumbnail of Phase transitions driven by competing interactions in low-dimensional systems

EPL (Europhysics Letters), 2010

Variable-temperature scanning tunnelling microscopy is used to study an orderorder phase transiti... more Variable-temperature scanning tunnelling microscopy is used to study an orderorder phase transition in a virtually defect-free quasi-one-dimensional surface system. The phase transition is driven by competing electronic interactions. The phase diagram is captured by a modified Landau formalism containing a coupling term between two different subsystems. The extra term has the effect of a spontaneously generated field which drives the phase transition. The proposed formalism applies to a variety of problems, where competing interactions produce sometimes counter-intuitive ordering phenomena.

Research paper thumbnail of Electronically driven phase transitions in a quasi-one-dimensional adsorbate system

The European Physical Journal B, 2010

A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface res... more A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface resonance structure is studied by angle-resolved photoemission spectroscopy for the clean surface as well as for different Bromine coverages. A Fermi surface mapping reveals saddle points at the Fermi level in the interior of the surface Brillouin zone. Correspondingly, a maximum in the static response function χ(q, 0) at the connecting vector q is expected. With 1/2Gx < q < 2/3Gx one observes indeed a 3-fold periodicity around defects and a 2-fold periodicity at low temperature for ΘBr = 0.5 ML. Cooling of a defect-free c(2 × 2)−Br/Pt(110) preparation counter-intuitively results in a loss of long-range order. Motivated by DFT calculations this is attributed to an anomalous order-order phase transition into the (2 × 1) phase accompanied by intense, strongly anisotropic fluctuations within a temperature range of ∼200 K. The peculiar behaviour is rationalised in terms of a competition between inter-adsorbate repulsion and an adsorbate triggered 2kF interaction in the substrate.

Research paper thumbnail of Magnetism and domain formation in SU(3)-symmetric multi-species Fermi mixtures

New Journal of Physics, 2011

We study the phase diagram of an SU(3)-symmetric mixture of threecomponent ultracold fermions wit... more We study the phase diagram of an SU(3)-symmetric mixture of threecomponent ultracold fermions with attractive interactions in an optical lattice, including the additional effect on the mixture of an effective three-body constraint induced by three-body losses. We address the properties of the system in D ≥ 2 by using dynamical mean-field theory and variational Monte Carlo techniques. The phase diagram of the model shows a strong interplay between magnetism and superfluidity. In the absence of the three-body constraint (no losses), the system undergoes a phase transition from a color superfluid phase to a trionic phase, which shows additional particle density modulations at half-filling. Away from the particle-hole symmetric point the color superfluid phase is always spontaneously magnetized, leading to the formation of different color superfluid domains in systems where the total number of particles of each species is conserved. This can be seen as the SU(3) symmetric realization of a more general tendency to phase-separation in three-component Fermi mixtures. The three-body constraint strongly disfavors the trionic phase, stabilizing a (fully magnetized) color superfluid also at strong coupling. With increasing temperature we observe a transition to a non-magnetized SU (3) Fermi liquid phase. arXiv:1012.4499v2 [cond-mat.quant-gas]